Rutherford County, TN Environmental Rules: Stormwater Management (2026)

Article III Section H of the Subdivision Regulations sets the engineering standards the County Engineer applies to every drainage system in a new unincorporated-county development. All stormwater infrastructure must sit in the public right-of-way or a recorded drainage easement; anything outside the right-of-way must be covered by a Maintenance Agreement recorded with the Register of Deeds before the final plat records. Before the County Engineer reviews any Construction Plans, the developer must submit full quantity and quality drainage calculations plus the Rutherford County Stormwater Calculation Summary.

Design follows the currently adopted Stormwater BMP Manuals, the Rutherford County Stormwater Ordinance, and TDOT Design Manuals unless the Subdivision Regulations state otherwise. On sizing, the Rational Method is allowed only up to a 50-acre drainage basin; larger basins need a County Engineer-approved alternative method. Post-development runoff cannot exceed pre-development rates for the 2-, 5-, 10-, 15-, 25- and 50-year storms, and the piping and channel network is designed to a 25-year storm frequency, with bridges also designed for the 25-year event. Detention and retention basins need hydraulic capacity for a 50-year event with an emergency spillway rated for the 100-year event, and stored volume must drain within 72 hours.

Direct discharge into waters of the state, as TDEC defines them, needs specific County Engineer approval. Outlet velocities cannot reach the erosive velocity of the receiving channel without added energy dissipation, and the design engineer must check the next two downstream structures and upgrade them if they cannot handle the new post-construction flow. 5 percent grade.